Metal implants have revolutionized the field of prosthetic dentistry and orthopaedics. The basic principle of implants is that screws, usually of titanium, are surgically inserted into human bones providing a foundation upon which a prosthetic device can be built. A metal implant system widely employed in prosthetic dentistry is the Branemark System, which is based on a discovery of Dr. Per-Ingvar Branemark.
A major disadvantage with present dental implant therapy, such as that of the Branemark System, is patient discomfort caused by two lengthy surgical procedures, with lengthy intervals being required between these procedures and final dental prosthesis insertion.
In the existing procedure a screw-like implant element is first inserted in a surgically formed bore in the bone and is then left for a period of about three to six months to permit the implant element to integrate or weld with the bone; the implant element has an internal threaded bore for subsequent threaded mounting of a support base or abutment for a prosthetic device. A temporary cover is applied over the exposed end of the implant element, so that the implant element is unloaded within the bone, beneath the gingival tissues.
When the implant element is adequately integrated or welded in the bore of the bone, the temporary cover is removed and the support base is threadedly attached to the implant element by way of the internal threaded bore so as to be disposed in a transmucosal abutment connection. After this attachment of the support base there is a further two to three week period to allow for healing of the tissue and integration of the support base with adjacent tissue, whereafter the prosthetic device is connected to the support base. It will be understood that the support base has an attachment for the mounting of the prosthetic device.
The existing procedures thus require significant time for completion, with the attendant discomfort and cost to the patient.
In orthopaedic surgery, much of the reconstructive therapy is based on the anchorage of metal prostheses in bone utilizing a space-filling bone cement, such as polymethylmethacrylate. This has been shown, however, to lead to osteocyte death due to mechanical, thermal and chemical injury. Eventual rejection may occur even if the implant is stably anchored to bone as the tissues are irreversibly damaged during the preparation of the recipient site. Furthermore, if the implant is connected to the external environment or immediately placed in function, both the initial loading stress and the ingrowth of microorganisms from the external environment lead to poor long-term prognoses.
Modifications of the implant design are being used in major facial reconstructive surgery. Implant therapy provides a foundation upon which prosthetic maxillofacial parts may be secured in patients who have become debilitated due to cancer, birth defects or traumatic injury.
Design considerations for implant assemblies for bone are described by Firoozbakhsh, K. K., et al: Bone Screw Design. Trans. of the Combined Meet. of the Orthopaedic Res. Soc. of U.S.A., Japan and Canada, Banff, AL, p. 222, 1991; Hayes, W. C.: Biomechanics of Cortical and Trabecular Bone. In Basic Orthopaedic Biomechanics (V. C. Mow and W. C. Hayes, editors). Raven Press, N.Y., p.93, 1991; Biomechanics. In Osseointegration in Dentistry, p. 37, 1993; Kay. J. F., et al: Stable HA Coatings for Non-Precision Implant Placement. Trans. of the Fourth World Biomaterials Congress, Berlin, Germany, p. 302, 1992; and Dziedzic, D. M. et al, Effects of Implant Surface Topography on Osteo-conduction. Trans. Fifteenth An. Meet. Canadian Biomat. Soc., Quebec, P.Q., p. 113, 1994; furthermore thread designs are described in 24th Edition, Machinery's Handbook (R. E. Green, editor). Industrial Press Inc. p. 1630, 1992.
DE Offenlengungschrift U.S. Pat. No. 3,325,666 describes a dental implant having a cavity extending from an upper end of a stem, but terminating in such upper end; a post is housed in the cavity and extends from the cavity to support a tooth implant.
U.S. Pat. No. 5,076,788 describes a cylindrical dental implant having grooves on its outer surface which communicate with openings extending inwardly into a chamber at a lower end of the implant. These openings provide passage for outflow of fluid and tissue from the jaw bone cavity to the grooves, such out-flowing material then flowing upwardly along the grooves